Electrostatic discharge events can destroy microelectronic circuits, so integrated circuit (“IC”) devices are commonly provided with such protection, normally on the IC chip (also called an IC die). On the chip, each diode is arranged so that any voltages on the I/O pad, which exceed the voltage of either the power supply or ground potential, cause conduction in the diodes, thus shunting the current induced by the voltage. Other than the momentary voltage drop of the diodes, the peak voltage seen by the internal logic of a semiconductor is limited. This technique is reasonably common and works well for many I/O circuits not requiring high-speed signal switching.
As semiconductor lithography has progressed over time and allowed finer transistor geometries to be manufactured, signal speeds have become increasingly limited by capacitive and resistive elements in semiconductor circuits. One source of unwanted capacitance stems from the ESD protection devices used in I/O buffers in semiconductors. An example of a typical ESD protection circuit 100 is shown in FIG. 1. The diodes 102 attached to the I/O pad 104 are in place to divert and redirect higher voltages appearing on the I/O pad away from the semiconductor chip device to either the power supply feed (“Vdd”) or the ground (“Gnd:). Unfortunately, the capacitance added by the addition of the diodes (inherent in the physics of the diode PN junction), makes the structure too slow for use in higher speed signaling that is in use today, and expected to increase in the future. One approach for decreasing the capacitance on an I/O buffer is to replace the diodes with bi-directional devices that have very low capacitance. As a solution, voltage switchable polymers, infused with conductive particles, have emerged and proved viable as a low-capacitance bi-directional ESD protection device.
Voltage switchable polymer based ESD protection devices are attractive due to their ability to provide protection at extremely low capacitance, as they can be desirably structured and fabricated in very small sizes. They can also be easily manufactured into printed circuit board and integrated circuit packaging substrates. However, one of the challenges is that as these voltage switchable polymer based ESD devices shrink, their ability to dissipate heat also declines. One result is that large ESD events can destroy voltage switchable polymer based ESD devices. While in the course of their destruction they may protect the integrated circuit one time, it is possible that many ESD events will occur over the life of the product, thus it is desirable to create an alternative structure that will address this shortcoming. Voltage switchable polymer based ESD protection devices are attractive for their small capacitance values.